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BASIC INSTRUCTION SET
A program contains instructions for the
NPX
in line with the instructions for
the
CPU. The system
executes these instructions in the same order as they appear in the instruction stream. The
NPX
operates
concurrently with the
CPU
to provide maximum throughput for numeric calculations.
The
software emulation
of
the
NPX
is
transparent to application software
but
requires more time for
execution.
3.12.1
Processor Extension Synchronization Instructions
Escape and wait instructions allow a processor extension such as the 80287
NPX
to obtain instructions
and
data
from
the
system bus and to wait for the
NPX
to return a result.
ESC
(Escape) identifies floating point numeric instructions and allows the 80286 to send the opcode
to
the
NPX
or to transfer a memory operand to the NPX. The 80287
NPX
uses
the
Escape instructions
to perform high-performance, high-precision floating point arithmetic
that
conforms to the
IEEE
float-
ing point standard 754.
Example:
ESC
6,
ARRAY
[SIlo The
CPU
sends the escape opcode 6 and
the
location of the array
pointed to by
SI
to the
NPX.
WAIT
(Wait) suspends program execution until the 80286
CPU
detects a signal
on
the BUSY pin.
In
a configuration
that
includes a numeric processor extension, the
NPX
activates the BUSY pin to signal
that
it has completed its processing task and
that
the
CPU
may obtain the results.
Example:
WAIT
3.12.2
Numeric Data Processor Instructions
This section describes the categories
of
instructions available with Numeric
Data
Processor systems
that
include a
Numeric
Processor Extension or a software emulation of this processor extension.
3.12.2.1
ARITHMETIC INSTRUCTIONS
The extended instruction set includes not only the four arithmetic operations (add, subtract, multiply,
and divide), but also subtract-reversed and divide-reversed instructions. The arithmetic functions include
square root, modulus, absolute value, integer part, change sign, scale exponent, and extract exponerit
instructions.
3.12.2.2
COMPARISON INSTRUCTIONS
The comparison operations are the compare, examine, and test instructions. Special forms of the compare
instruction
can
optimize algoriihms
by
ailuwiug
cOiilpafisuii5
of
binary
integer:;
....
ith
real
r.:um.ber~
in
memory.
3_12.2.3 TRANSCENDENTAL INSTRUCTIONS
The
instructions in this group perform the otherwise time-consuming calculations for all common
trigonometric, inverse trigonometric, hyperbolic, inverse hyperbolic, logarithmic, and exponential
functions. The transcendental instructions include tangent, arctangent,
2
x-I,
Y .
log2X,
and Y.
log2
(X+l).
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